Electrical switch focused in combustible atmospheres

ABSTRACT

An electrical switch adaptable for use in combustible atmospheres in which make and break circuit functions are performed within a compact housing sealed from its environment and under the direction of a movable switch member controlling the transfer of radiant energy, thereby making explosion-proof devices simple and economical to manufacture and install as the movable member may be an arcless component situated external to the insulated housing.

United States Patent 1191 Long et al. I I

1451 Apr. 16,1974

Tums 200/168 G ELECTRICAL SWITCH FOCUSED IN 3,385,945 5/1968 COMBUSTIBLE ATMOSPHERES 3,681,553 8/1972 Lehman et a1..... 200/ 168 G 3,459,943 8/1968 Hamden, Jr....... 250/206 X [75] Inventors: Donald 0- ong, d y, a; 3,529,214 9/1970 Corn 250/206 x Albert C. Hartsough, Willingboro; 3,584,222 6/1971 Nesbitt... 250/214 R Robert F. Sanford, Princeton 3,588,512 6/1971 Hollien 250/229 X Junction, both of NJ. [73] Assignee: Princeton Electro Dynamics, Inc., Primary Examiner-Walter Stolwein Princeton Junction, NJ.

22 F'l d: 10 1972 1 1 e Jan 57 ABSTRACT [21] Appl. No.: 216,527

An electrical switch adaptable for use in combustible atmospheres in which make and break circuit func- [52] Cl 250/206 y tions are performed within a compact housing sealed Int Cl j 39/12 from its environment and under the direction of a movable switch member controlling the transfer of ra- [5 8] Fleld of Search 250/ d %z diant energy, thereby making explosion-proof devices simple and economical to manufacture and install as the movable member may be an arcless component [56] References Clted situated external to the insulated housing.

UNITED STATES PATENTS 3,364,318 1/1968 Bulliet 200/47 3 Claims, 10 Drawing Figures zz zo 54 M 4 26 61 32 1 0W! 14/- 2 S Jflflifi /e /Z J! 40 b PATENTEUAPR 16 1974 SHEET 2- BF 2 FIG.6.

Fis.9.

I 14 I512 I098 ELECTRICAL SWITCH FOCUSED IN COMBUSTIBLE ATMOSPHERES FIELD OF THE INVENTION This invention relates to electrical make and break switches, in general, and to explosion-proof, arcless electrical switches for use in combustible, gaseous atmospheres, in particular.

SUMMARY OF THE INVENTION As will become clear hereinafter, the constructions of the invention permit such devices to be more economically manufactured and more easily installed then were heretofore possible. Reduction in manufacturing costs will be seen to follow from the use of a movable, arcless make and break switch control which is external to the housing employedspace and weight requirements for the housing can thus be lessened. Ease of installation will also follow this reduction in size and bulk, and will further follow from the elimination of the need to insulate the movable switch component from the combustible atmosphere-as was previously required with conventional make and break contacts.

These advantages both result with a construction in which the make and break electrical functions are performed within a sealed housing, but under the direction of a switch component which regulates the transfer of a radiant optical, magnetic, or heat energy, for example, to establish the electrical control, rather than the previously employed transfer by the switch component of the electrical energy itself. Thus, a light shutter is employed in one embodiment of the invention to control the illumination of a photocell in completing an electrical circuit, with the source of optical energy and the photo-sensitive device being both included within the housing but with the shutter being external to the housing and the component which is not subject to arcing in opening or closing the circuit. Similarly, a nonarcing, external magnetic arrangement is employed in a second embodiment of the invention to control the closing and opening of a reed switch within the housing in making and breaking an electrical circuit. A temperature sensing device is utilized in a third embodiment in establishing the switch function, also in response to the direction from an arcless control, in this case, the proximity of a heat source.

Such methods of employing non-electrical types of control in regulating the transfer of electrical energy will be seen to facilitate the construction of explosionproof switches for use in oil refineries, in chemical installations and in oxygen rich hospital rooms, for example. Depending upon the power handling capabilities of the types of sensors and/or switch components employed, such switches can find use in applications extending from large circuit breaker installations down to the every day type of wall switch, and beyond. While particularly suited for use in combustible atmospheres,

the arrangements of the invention are sufficiently low in price to make them-attractiveas protective substitutes for non-critical uses, as well.

BRIEF DESCRIPTION OF THE DRAWINGS These and other features of the present invention will be more readily understood from a consideration of the following description taken in connection with the accompanying drawings in which:

FIGS. 1-4 are schematic diagrams of embodiments of the invention in which the transfer of optical energy is regulated by a light shutter or vane to control the make and break functions of an electrical switch;

FIG. 5 shows, in partial form, a modification of the light shutter of FIGS. 1-4, which permits a simplification to be made in the schematic embodiments thereof;

FIG. 6 shows a housing for the embodiments of FIGS. 1-4, including the positional relationship between the electrical circuit components of the switch within the housing, and the mechanical light shutter control which is external thereto;

FIGS. 7 and 8 are schematic diagrams of other embodiments of the invention in which the transfer of magnetic energy is regulated to control the make and break functions of an electrical switch;

FIG. 9 shows, in partial form, a modification of the magnetic energy construction of FIG. 7 to utilize the transfer of heat energy in the closing and opening of electrical switches; and

FIG. 10 illustrates typical arrangements for sealing the electrical components of the switch from its surrounding environment, so as to facilitate its use in combustible, gaseous atmospheres.

DETAILED DESCRIPTION OF THE DRAWINGS In FIG. 1, the optical energy to be transferred in establishing the electrical circuit connection is provided by a neon lamp 10. A power sourcerepresented by the terminals 16, 18-is coupled across the opposite electrodes 12, 14 of the lamp 10, with the terminal 16 being directly connected to the electrode 12 and with the terminal 18 being coupled to the electrode 14 by the series connection of a resistor 20 and a rectifier 22. As shown, the cathode electrode of rectifier 22 is connected directly to the terminal 18 while the anode electrode of the rectifier device is connected, on the one hand, to resistor 20 and, on the other hand, via a capacitor 24 to the lamp electrode 12.

Also shown in FIG. 1 are alight sensing photocell 26 and a Triac (or bidirectional triode thyristor) 28. One electrode 30 of the photocell 26 is connected to a first power electrode 32 of the Triac 28 and, further, to an output terminal 34 which serves as one contact a of the electrical switch of the drawing. A second electrode 36 of photocell 26 is connected to the gate electrode 38 of the Triac 28, while the second power electrode 40 of Triac 28 is connected to an output terminal 42 which serves as a second contact b of the switch. A utilization circuit 44 is, in turn, coupled across contacts a and b, so that the Triac 28 conditioned to a low impedance state, electrical power applied to contact a can be used to energize the circuit 44 into operationsuch as the illumination of an incandescent lamp circuit 44 with the application of an alternating voltage to contact a. Additionally shown in the drawing in representative form is a light shutter or vane 46, which can be mechanically moved, as desired, to regulate and control the amount of illumination .impinging on the photocell 26.

In one construction of the FIG. 1 embodiment, a cadmium-sulphide type device can be employed as the photocell 26, to exhibit a resistance characteristic which varies inversely as a function of the amount of incident light. When the light impinging on the surface of the photocell 26 increases, the resistance of the photocell decreases to raise the instantaneous voltage on the gate electrode 38of the Triac 28 measured with respect to the power electrode 40. This reduces the breakover voltage needed for application to power electrode 32 to switch Triac 28 from its high impedance state to its low impedance state. With sufficient light impinging the photocell surface, the Triac 28 can be triggered on each half-cycle of the alternating power source to supply power to the utilization circuit 44 as long as the light impinges the photocell 26 to keep its resistance low. As will be readily apparent, moving the light shutter 46 to reduce the incident light will increase the resistance of photocell 26 and lower the voltage on the gate electrode 38 of the Triac 28-and will eventually switch triac 28 back to its high impedance state and render it non-conductive to open the electrical path for circuit 44. Light shutter 46 thus serves as the actuating member of the electrical switch illustrated, but, itself, gives rise to no arcing possibilities as contact is to be made or broken. For this reason, the movable member of this switch may be located outside the sealed housing and within an explosive atmosphere where circuit control is needed--but without the fear that its actuation will itself give rise to an ignitable spark.

The embodiments of the invention shown in FIGS. 2 and 3 utilize an integrated circuit in establishing the control voltage for the gate electrode 38 of the Triac 28 so as to provide a controlled operation free from any transients which might be present on the alternating current power line. With a Triac 28 of 2N5574 type designation, for example, the use of a monolithic integrated circuit to apply a trigger voltage to the Triac gate electrode 38 whenever the supplied power line voltage reaches a zero-axis crossing has been found to be particularly attractive in suppressing transient electrical switchings. Such an integrated circuit is described in the publication of the Electronic Components Division of the RCA Corporation under its file designation No. 397, entitled Zero-Voltage Switch-CA3059.

Thus, in each of FIGS. 2 and 3, output terminal 4 of device CA3059 (reference numeral 50) is directly connected to the gate electrode 38 of Triac 28 whereas terminals 2 and 13 of the monolithic device couple to the photocell 30, 36, respectively. A first resistor 52 interconnects terminals 8 and 13 of the integrated unit 50, with terminal 8 being in turn connected to terminal 7 of the monolithic circuit and to the power source terminal 16 for the illuminating lamp. A capacitor 54 commonly couples source terminal 16 to terminals 2 and 3 of the integrated device 50 in each drawing where, as shown, terminals 9-11 are short-circuited while terminals l, 6, 12 and 14 are open-circuited in each arrangement. The specific circuit diagram for the electrical components interconnecting these device terminals is shown in the aforesaid publication, whose disclosure is herein incorporated by reference. With respect to FIG. 2, furthermore, a neon illuminating lamp 56 is employed, having a first electrode 58 coupled by a second resistor 60 to the power source terminal 18 and a second electrode 62 connected to the source terminal 16. A third resistor 64, coupled between the power source terminal 18 and terminal 5 of the monolithic integrated circuit 50 completes the FIG. 2 arrangement. A second resistor 66, on the other hand, completes the FIG. 3 configuration by coupling one end of an incandescent illuminating lamp 68 to the power source terminal 18,

with the other end of lamp 68 being directly coupled to terminal 5 on the integrated device 50. The load circuit for each of these constructions may be the same as in FIG. 1.

With the device of the RCA publication, trigger pulses are generated at terminal 4 of the integrated circuit unit 50 in response to the zero-axis crossing of an alternating voltage applied, as in FIGS. 2 and 3 herein, across its input terminals 5, 7. Such action is controllable by an included differential amplifier, to the extent that an output can be generated only if the voltage developed across terminals 13 and 7 exceed a reference voltage existent between terminals 9 and 7 of the device by prescribed amounts. With the inclusion of photocell 26 and resistor 52 in the circuits of FIGS. 2 and 3, a voltage divider network is formed which effectively varies the potential at terminal 13 as a function of the amount of light impinging its surface. More particularly, with the connections illustrated, decreases in the incident light serve to increase the resistance of the photocell 26, and in a direction to lower the terminal 13 potential relative to terminal 9 to a value within one of the two conductive ranges of the device 50 to permit the generation of the trigger signal for the Triac 28. Increases in the incident light, on the other hand, raise the potential at terminal 13 relative to terminal 9 outside this range and inhibit the generation of the output trigger.

As with the configuration of FIG. I, a light shutter or vane 46 is included to regulate the amount of illumination reaching the photocell 26 from lamps 56 or 68. Moving the shutter 46 to impede the necessary transfer of optical energy to the photocell surface to condition the differential amplifier of the monolithic device 50 thus produces the needed trigger to fire the Triac 28. v

and close the circuit path for the utilization apparatus 44, here coupled between terminal 18 and terminal 34 coupled to Triac electrode 32. Conversely, moving shutter 46 to permit the transfer of optical energy prevents the generation of the needed trigger and the electrical switch, in such mode of operation, becomes open-circuited. Light shutter 46 again serves thusly as the actuating member of the switch, but since it itself carries no electrical charge, its movement to make or break a circuit does not give rise to the development of an electrical arc to it as the opening or closing of the circuit occurs. The controlling shutter can once again be placed outside the housing sealing the possible spark producing Triac, photocell, and electrical circuit elements from a combustible atmosphere, thereby greatly simplifying the overall switch design while maintaining the required immunity from possible gaseous ignition.

It will be readily apparent to those skilled in the art that by interchanging the photocell 26 and resistor 52 in the FIGS. 2 and 3 constructions, the light shutter control can be reversed. The placements of these two components in the voltage divider network for terminal 13 of the monolithic chip 50 will then be inverted-- -increasing illumination impinging the surface of the photocell 26 will thus raise the potential at terminal 13 relative to the potential at terminal 9 to the second conductive range for the device 50 and permit the generation of the circuit closing trigger for the Triac 28 while decreasing illumination will have the opposite effect. With either of the two arrangements illustrated in FIGS. 2 and 3--and, also, with either of the arrangements of FIGS. 1 and 4-5 to be discussed below-, a fibre optic light pipe can be constructed in conjunction with the light shutter 46 (as exemplified in FIG. 1 by the reference numeral 200), to provide a pilot lamp indication as to the present state of the switch. Such indication is particularly attractive where the switch is employed to control an electrical apparatus at a remote location.

The embodiment of the invention shown in FIG. 4 is useful in instances where it is desired to suppress radio frequency interference produced by the switching action of the Triac on each half-cycle of the alternating input voltage. Here, the first power electrode 32 of Triac 28 is coupled to the input terminal 18 via a choke 70 while a capacitor 72 couples the second power electrode 40 to that terminal. A resistor'60 and neon lamp 56 are, as in FIG. 2, coupled between input terminal 16 and 18, and combine to illuminate the photocell 26 of the construction, again under the control of the light shutter vane 46. With photocell 26 coupled between the power electrode 32 of Triac 28 and its gate electrode 38, the arrangement is completed by the connection of a resistor 74 across the electrodes 38 and 40. The utilization apparatus 44 may be connected between the Triac terminal 42 and reference terminal 16.

As in the embodiment of FIG. 1, increases in the amount of light impinging the surface of the photocell 26 decreases its resistance so as to raise the instantaneous voltage on the Triac gate electrode 38 with respect to the power electrode 40. This voltage divider action of photocell 26 and resistor 74 again permits the alternating voltage applied to the power electrode 32 to trigger the Triac 28 and effectively close the switch with sufficient light illumination. With decreasing light, on the other hand-as where the shutter 46 is interposed between photocell 26 and lamp 56, insufficient voltage'will be coupled to gate electrode 38 to permit firing of the Triac 28 with the amplitude of applied input voltage. The choke 70 and capacitor 72, in this instant, comprise a filter which attenuates any high frequency radio interference which might otherwise be coupled back through the alternating current power lines through other equipments operating therefrom. Because the response time of the cadmium sulphide photocell 26 is slower than the period of a 60 cycle alternating input voltage, for example, application of such alternating signal to illuminate the neon lamp 56 in these embodiments will not detract from the described operations as the photocell will maintain the Triac 28 in its low impedance state even though the lamp 56 is switching on and of with each input half-cycle.

Whereas the embodiments of FIGS. 1 and 4 each operate when the light shutter 46 is retracted to expose the photocell 26 to the illuminating lamp, it will be apparent that modifications may be made to the configurations (as noted with respect to the arrangements of FIGS. 2 and 3) so that actuation of the vane in the opposite direction can constitute the switch closure. One such modification which greatly simplifies these constructions is partially illustrated in FIG. 5. Here, instead of using a vane 46 to controllably shutter the optical energy transferred from a light source to a photocell, this movable member itself comprises the source of illumination. By surfacing the vane 46 with a light emitting material, e.g., a phosphor dot, in the proximity of the photocell 26, effective control of the electrical switch follows the consequent movement of the vane adjacent to and away from the photocell 26. While a fibre optic array is no longer usable in this arrangement to indicate the position of the switch, other means of identification can be employedsuch as an additional phosphorescent material placed on the moving vane which comes into view when the switch is thrown to its operative position.

FIG. 6 illustrates a housing into which the electrical components of the switchphotocells, illuminating lamps, Triacs, resistors, capacitors, etc.-are inserted, and then sealed from the surrounding environment. The photocell 26 and Triac 28 of the previous embodiments are schematically represented as being in an upper portion 101 of the housing 100, while the illuminating lamp 56 is situated in a lower portion 102. Three screw contact connections are illustrated, one, 103 serving as a ground connection for the lamp 56, a second, 104 serving as a load connection for the utilization network 44 and the third, 105 serving as the input terminal for the energized conductor to be connected through the switch to contact 104. A slot or apertured opening 106 with sealed means to permit passage of light across 106 is provided in the housing 100 to accept the light vane 46 as it is moved into and out of the breach to controllably shutter the light from lamp 56 impinging on the photocell 26. It will be appreciated that specific manners of detenting shutter mechanisms to permit or block the transfer of radiant energy in the foregoing or subsequent embodiments of the invention form no part of the present description, but are ancillary thereto. I-Iowever--and in accordance with the invention-, this controllable transfer of radiant energy by a shutter mechanism which is, in itself, incapable of producing a spark during its movement in making or breaking an electrical circuit permits its removal from the sealed housing, to thereby yield a significant reduction in the size and bulk of prior art switches used in combustible atmospheres where the electrically ener-- gized switched member was capable of arcing both in opening and closing the circuit contacts. FIG. 10, below, illustrates a manner in which the screw contact connections 103-105 may be insulated from the atmosphere, also, but in passing, it will be noted that where the movable vane is of the type which itself provides the photocell illumination (FIG. 5), the bottom portion of the housing 102 and its component parts may be eliminated.

FIGS. 7 and 8 show alternative embodiments of the invention, similar to those of FIGS. 3 and 4 respectively, but different therefrom in its use of magnetic,

' rather than optical energy to control the switch condition. Thus, in FIG. 7, it will be seen that the same type of zero-voltage integrated circuit switch 50 is employed as in FIG. 3, with identical connections to the Triac 28 and from the input terminals l6, 18, with one exception. That is, instead of terminal 5 of the monolithic device 50 being coupled to terminal 18 via a resistor 66 and a lamp 68-as in FIG. 3, the coupling from terminal 5 to the input terminal 18 is directly through a resistor, here 110. Additionally different in FIG. 7 as compared to FIG. 3 are the series coupling of a resistor 112 and reed switch 114 from integrated chip terminal 7 to integrated chip terminals 13 and 14 in common connection and the inclusion of a further resistor 116 between chip terminals 2 and 13. Lastly, a movable magnet 118 is used to control the state of the reed switch 114 in much the same manner as the light shutter 46 of FIG. 3 controls the photocell 26.

Thus, in FIG. 7, it will be noted that moving the magnet 118 to the vicinity of reed switch 114 to establish sufficient magnetic flux as will close the switch 114 will additionally place the further resistance of resistor 112 between chip terminals 13 and 7. As this will tend to lower the potential developed at terminal 13 relative to that developed at chip terminal 9 to the first of the conductive ranges for the device 50, the effect will be to enable the control afforded by the differential amplifier of the zero-crossing switch 50 and permit the generation of the trigger signal for the Triac 28. The potential provided at chip terminal 13 with the reed switch 114 open, on the other hand, is regulated by resistor 116 to impede the generation of the trigger pulse at terminal 4 of the monolithic chip 50. Moving the magnet 118 in FIG. 7 to control the condition of reed switch 114 is analogous, therefore, to the movement of the light shutter 46 in FIG. 3 to control the photocell 26. It will be seen, however, that whereas in FIG. 7 the transfer of magnetic energy to the control element actuates the electrical switch for the utilization circuit 44, in FIG. 3

the transfer of optical energy to the sensor disabled the switch.

The configuration of FIG. 8, on the other hand, will be seen similar to the FIG. 4 construction in its coupling of the radiant energy sensing circuit between the first power electrode 32 of the Triac 28 and its gate electrode 38, but different from that showing in a number of respects. Thus, the photocell 26 of the FIG. 4 arrangement is replaced in FIG. 8 by the series coupling of a resistor 130 and a reed switch 132 while the voltage divider resistor 74 coupling the gate and second power electrode 38, 40 is omitted. Additionally, the optical energy source circuit including the resistor 60 and neon lamp 56 coupled between terminals 16 and 18 in FIG. 4 is replaced by a detenting magnetic energy source, represented by the movable magnet 134.

It will be readily apparent that this arrangement, with its radio frequency interference choke 70 and filter capacitor 72, is exceedingly simple to construct. Detenting the magnet 134 to establish sufficient magnetic flux to close the reed switch 132 couples a portion of the alternating signal applied to input terminal 18 to the gate electrode 38 of the Triac 28 to eventually trigger it to its low impedance state and effectively couple that input signal to the output terminal of the switch 34. By making the detent mechanism of a plastic, nonconducting material, for example, no moving parts are available to rub against each other in adjusting the magnet position in controlling the closure of the reed switch 132. As a result, this radiant energy magnet can also be placed in a gaseous, combustible atmosphere-- external to the sealed housing enclosing the choke, capacitor, triac and other electrically operative elementsand its regulation not give rise to an ignitable spark. In this construction then, moving the radiant magnet source 134 adjacent the reed component 132 will close the electrical switch without the danger of any arcing, and permit-as in the foregoing arrangementsthe removal of the actuating switch member from the insulated housing to permit reductions to be made in its size and bulk.

The radiant heat energy configuration of FIG. 9 also employs the zero-axis crossing integrated chip 50 of FIG. 7, with similar couplings between terminals of the device and to external out-board components. A first resistor is once more employed to couple the input terminal 18 to the chip terminal 5, while device terminals 2 and 3 are commonly connected again via a second resistor 142 to chip terminals 13 and 14 and via a capacitor 144 to a reference terminal for the switch 16. A load circuit is again coupled between power electrode 32 of Triac 28 and input terminal 16, and the energy sensing circuit is, as before, coupled between the terminals 13 and 7 of the monolithic circuit 50 to control the development of the trigger pulse output. Because radiant heat energy is employed to control the making and breaking of the electrical switch, the sensing circuit of FIG. 9 comprises a thermistor type of temperature controller and a detentable resistor 152 through which current is caused to flow to produce a power dissipation there-across.

In operation of this configuration, moving the power dissipating resistor 152 adjacent the thermistor 150 raises its temperature and causes a decrease in its exhibited resistance. The increased loading which occurs at terminal 13 of the monolithic chip 50 results in a decrease in the potential at the terminal 13 relative to the device terminal 9 to its first conductive range to enable the operation of the included differential amplifier and permit the generation of the trigger signal for the Triac 28. Moving the resistor 152 away from thermistor 150, on the other hand, causes the resistance exhibited by the latter to increase until the loading at the differential amplifier is reduced to the point at which trigger pulses will again be disabled for the Triac 28 and open the switch between input and output terminals 16, 34. By applying a continuous current flow through resistor 152, it, too, will serve as the actuating member of the switch construction, making and breaking an electrical circuit in an arcless manner. Its use in a combustible atmosphere is therefore possible, and particularly so when the heat generated by the current flowing through the resistor is substantially below that which would ignite the gaseous vapor. The detentable resistor 152 could-like the light shutter vane of FIGS. 1-5 and the magnet of FIGS. 6-7-be inserted for movement within the apertured slot 106 of a housing such as in FIG. 6, to control the temperature sensor sealed within that construction and insulated from the ignitable surroundings. Preferably, the resistor l52 should be made of a heat conductive material (e.g., ceramic), which would undergo temperature variations with supplied current without being moved back and forth-in this way, the possibility of breakage of lead connections could be reduced, and arcing thereby further prevented.

The representations of FIG. 10 illustrate a housing for the switch of the invention, and particularly apertures and 171 thereof through which the electrical cable wires pass in powering the electronics of the switch. Connections of these wires to the illustrated screw contacts 172, 173 are then made, to which the various resistive, capacitive, Triac, etc., components are coupled. After such connections are made, the entire volume surrounding the screw contact may be encapsulated, with an insulating epoxy resin for example, to effectively seal both the contact of the switch and the energized lead wires of the electrical power connectors from the environment surrounding the housing. The switch is then ready for installation in an ignitable environment, and when controlled by any of the foregoing radiant energy manners, will provide explosionproof make and break circuit operation.

Besides the advantage of reduced size and bulk which flows from the placement of the actuating member of the switch external to the housing, there also follows the advantage of increased ease of installation. Because of its smaller size, the housing will easily fit within the usual wall socket used for light switches and, because of the simplicity of construction which permit manu facturing costs only one and one-half or so timesgreater than such typical arrangements (as in FIG. 8), such switches serve as ready substitutes for those previously used while providing additional arcless operating advantages. Master control of these switches is also easily attainableby cutting off all power to the many neon lamps in installations employing constructions as in FIG. 1, for examplewithout the need of running special heavy duty cables back and forth throughout the installation to the master switch control. This feature is particularly attractive in that the shutdown can be effected at the remote location without mechanically moving the light shutter-or magnet or heat source for that matter-, again without the danger of any electrical sparking.

While there have been described what are considered to be preferred embodiments of the invention, it will be apparent to those skilled in the art that other modifications may be made without departing from the teachings herein of using the mechanical control of radiant energy in the making and breaking of electrical switch contacts. Thus, toggle arrangements can be employed with the light shutter, magnet or heat source configurations to provide a push-button type of construction or selective rotary positional structures can be employed to provide rotary motion switches. Multi-pole switch fabrications will also be apparent, as will the utilization of different combinations of radiant energy sources to reflect the multiple controls envisionablethus, one multiple pole construction according to the invention might utilize a single neon lamp anda plurality of photocells and light shutters, while another might use a plurality of lamps or a combination of lamps and magnets or heat sources. Hall effect devices might also be employed as similar sensors and, as with the illustrated embodiments, will respond to the mechanical control of radiant energy incident upon it to establish the switch constructions without arcing. These alternative arrangements will each be seen to be encompassed by the disclosure herein and are to be read in the light of such descriptions.

What is claimed is:

1. An electrical switch for use in a combustible atmosphere comprising:

a housing and means sealing said housing against said combustible atmosphere, said housing containing an electronic switching circuit including 5 first and second power terminals for connection to a utilization circuit; and

actuating means which make for making electrical connection between said terminals when said switching circuit is closed and which break said electrical connection when said switching circuit is open;

said actuating means including:

a. a source of illuminating energy;

b. an illumination detector having an input terminal coupled to said first terminal and an output terminal coupled to said second terminal and being electrically placed in one of a low and high impedance state between its input and output terminals in making and breaking said connections as a function of the magnitude of illuminating energy radi-ated thereon from said source; and

c. mechanical regulator means positioned with respect to said source of illuminating energy for mechanically controlling the amount of illuminating energy impinging upon said illumination detector from said source and the actuation of said switching circuit from a make to a break condition and vice versa;

with at least said first and second terminals and said illumination detector and said source being subject to electrical arcing, but being included within said housing and therefore sealed from said combustible atmosphere, and with said mechanical regulator means being non-electrically operable and therefore not subject to arcing being wholly external to said housing and within said atmosphere, to thereby control said switch from closed condition to open condition solely from within said combustible atmosphere but without giving rise to the creation of such electrical arcs as would tend to ignite said atmosphere.

2. The arcless switch of claim 1 wherein said regulator means includes light shuttering apparatus for controlling the amount of illumination impinging upon said detector in actuating said switching circuit to its closed and open conditions.

3. The switch of claim 2 wherein said illumination detector comprises a photocell exhibiting a resistance characteristic which varies inversely with the amount of illumination impinging thereon.

- UNETED STATES PATENT OFFICE CERTI'FlQATE 0F CORRECTION Patent No. 3'805I059 Dated April H1974 Inventor(s) Donald C. long, et a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the title, both on the title page and in Column 1, "FOCUSED" should read FOR USE 1 Column 2, Line 52 a and b should read "a" and "b".

Column 2, Line 53 v a e should read "a".

a should read "a".

Column 2, Line 57 electrodes should be inserted after "photocell".

Column 3, Line 45 Column 3, Line'64 2532mm should be inserted after Column 4, Line is t j on should be inserted after "impinging".

Column 4, Line 60 on should be inserted after "impinging".

001mm 5, Line 17 v should read "terminals". Column 5, Line 41 instant should read "instance". Column 6, Line 27 breach should read "breech". Column 10, Line 21 Q radi-ated should read "radiated".

Signed and sealed this 12th day of November 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM F'O-1050 (10-69) USCOMM'DC madam 3530 6'72 w us. GOVERNMENT rnm'rms OFFICE: 1969 0-366-334 

1. An electrical swiTch for use in a combustible atmosphere comprising: a housing and means sealing said housing against said combustible atmosphere, said housing containing an electronic switching circuit including first and second power terminals for connection to a utilization circuit; and actuating means which make for making electrical connection between said terminals when said switching circuit is closed and which break said electrical connection when said switching circuit is open; said actuating means including: a. a source of illuminating energy; b. an illumination detector having an input terminal coupled to said first terminal and an output terminal coupled to said second terminal and being electrically placed in one of a low and high impedance state between its input and output terminals in making and breaking said connections as a function of the magnitude of illuminating energy radi-ated thereon from said source; and c. mechanical regulator means positioned with respect to said source of illuminating energy for mechanically controlling the amount of illuminating energy impinging upon said illumination detector from said source and the actuation of said switching circuit from a make to a break condition and vice versa; with at least said first and second terminals and said illumination detector and said source being subject to electrical arcing, but being included within said housing and therefore sealed from said combustible atmosphere, and with said mechanical regulator means being non-electrically operable and therefore not subject to arcing being wholly external to said housing and within said atmosphere, to thereby control said switch from closed condition to open condition solely from within said combustible atmosphere but without giving rise to the creation of such electrical arcs as would tend to ignite said atmosphere.
 2. The arcless switch of claim 1 wherein said regulator means includes light shuttering apparatus for controlling the amount of illumination impinging upon said detector in actuating said switching circuit to its closed and open conditions.
 3. The switch of claim 2 wherein said illumination detector comprises a photocell exhibiting a resistance characteristic which varies inversely with the amount of illumination impinging thereon. 